1. Field of the Invention
The present invention relates to an improved method for treating radioactive organic wastes by a wet-type oxidative decomposition process.
2. State of the Art
Waste water occurring in nuclear power plants or laboratories handling radioactive substances is disposed after being filtered and treated with ion-exchange resins. It is necessary to treat the radioactive spent filter sludge and spent ion-exchange resin for safe disposal thereof.
To date, the proposed methods for volume-reducing this kind of radioactive organic waste, include dry processes as incineration and thermal decomposition, and wet processes as acid digestion and the so-called Zimmerman Process. All of the known methods have obstacles, which prevent their commercial practice.
The incineration method inevitably generates a large amount of corrosive exhaust gas, which thereby requires a large scale treating system. Further, additional problems remain to be solved before applying this method to the radioactive waste.
The thermal decomposition method is advantageous due to the easy treatment of the exhaust gas because only a small amount of radioactive nuclear species transfers to the decomposed gas. However, the entire process is complex since treatment of the decomposed gas requires a combination with the incineration method.
The acid digestion method using concentrated sulfuric acid has an advantage in that, a major portion of the radioactive substances remains in liquid, thereby making it easy to treat the exhaust gas. The objectionable feature is that the method suffers from severe corrosion of the apparatus necessitating expensive material for the apparatus, such as tantalum.
The Zimmerman Process has the same advantage, though precautionary measures for ensuring safety under the operation conditions of high pressure and high temperature are necessary.
Utilization of the hydrogen peroxide aqueous solution for treating the spent cation-exchange resin has been attempted with reported results that show ferric ion Fe.sup.3+ takes the role of a catalyst to promote this oxidative decomposition reaction (See the report "Decomposition of Ion-Exchange Resins with Hydrogen Peroxide" by Kubota et al. for The Japan Association of Nuclear Power held on Mar. 28, 1981). This catalytic oxidative decomposition is, however, not as useful when applied to the treatment of an anion-exchange resin because decomposition thereof does not readily proceed.